1) Вычислить: 2 1/2 · (2/75 − 3 5/6) + 1/4; 2) Вычислить: −1 1/2 · (4/5 + 19/20) · (6 5/6 + 4 2/3).

\(2\dfrac{1}{2}=\dfrac{5}{2}\), \(3\dfrac{5}{6}=\dfrac{23}{6}\).

\[\dfrac{5}{2}\left(\dfrac{2}{75}-\dfrac{23}{6}\right)+\dfrac{1}{4}=\dfrac{5}{2}\left(\dfrac{4}{150}-\dfrac{575}{150}\right)+\dfrac{1}{4}=\dfrac{5}{2}\cdot\left(-\dfrac{571}{150}\right)+\dfrac{1}{4}=-\dfrac{571}{60}+\dfrac{1}{4}=-\dfrac{571}{60}+\dfrac{15}{60}=-\dfrac{556}{60}=-\dfrac{139}{15}.\]

Ответ: \(-\dfrac{139}{15}=-9\dfrac{4}{15}\).

\(-1\dfrac{1}{2}=-\dfrac{3}{2}\), \(6\dfrac{5}{6}=\dfrac{41}{6}\), \(4\dfrac{2}{3}=\dfrac{14}{3}\).

\[\left(\dfrac{4}{5}+\dfrac{19}{20}\right)=\dfrac{16}{20}+\dfrac{19}{20}=\dfrac{35}{20}=\dfrac{7}{4},\]

\[\left(\dfrac{41}{6}+\dfrac{14}{3}\right)=\dfrac{41}{6}+\dfrac{28}{6}=\dfrac{69}{6}=\dfrac{23}{2}.\]

\[ -\dfrac{3}{2}\cdot\dfrac{7}{4}\cdot\dfrac{23}{2}=-\dfrac{3\cdot7\cdot23}{16}=-\dfrac{483}{16}=-30\dfrac{3}{16}.\]

Ответ: \(-\dfrac{483}{16}=-30\dfrac{3}{16}\).